Procedure for fabricating ultra-small gold wire

ABSTRACT

The procedure for fabricating ultra-small precious metal or metal alloy wire comprising the steps of fabricating and annealing a copper sleeve with an axially aligned opening formed therein, forming and annealing a precious metal core and inserting the core into the opening, the sleeve and the core having outer dimensions preferably formed in the ratio of ten to one, mechanically binding the core to the sleeve to produce a bimetallic wire combination, reducing the size of the wire combination on suitable wire drawing dies and then chemically removing the sleeve from the precious metal wire.

United States Patent [191 Hendrickson Nov. 19, 1974 PROCEDURE FORFABRICATING ULTRA-SMALL GOLD WIRE [75] Inventor: Paul E. Hendrickson,Wayne, Pa.

[73] Assignee: Albert A. Ciardi, Jr., Philadelphia,

Pa. a part interest [22] Filed: Mar. 8, 1973 [21] Appl. No.: 339,306

[52] US. Cl 29/423, 29/D1G. 11, 29/419 [51] Int. Cl B23p 17/00 [58]Field of Search 29/423, 424, 419, DIG. 11

[56] References Cited UNITED STATES PATENTS 2,050,298 8/1936 Everett29/180 X 2,215,477 9/1940 Pipkin 29/423 X 7/1971 Roberts et al. 29/423 XPrimary Examiner-C. W. Lanham Assistant Examiner-Victor A. Di PalmaAttorney, Agent, or Firm-Karl L. Spivak, Esq.

[ 5 7] ABSTRACT The procedure for fabricating ultra-small precious metalor metal alloy wire comprising the steps of fabricating and annealing acopper sleeve with an axially aligned opening formed therein, formingand annealing a precious metal core and inserting the core into theopening, the sleeve and the core having outer dimensions preferablyformed in the ratio of ten to one, mechanically binding the core to thesleeve to pro duce a bi-metallic wire combination, reducing the size ofthe wire combination on suitable wire drawing dies and then chemicallyremoving the sleeve from the precious metal wire.

7 Claims, 6 Drawing Figures PATENIQ, rm 1 91974 FIG. 4

FIG. 6

- FIG PROCEDURE FOR FABRICATING ULTRA-SMALL GOLD WIRE BACKGROUND OF THEINVENTION This invention relates in general to the field ofmanufacturing fine wire, and more particularly, is directed to aprocedure for fabricating ultra-small gold wire.

In the production of ultra fine wire, prior workers in the art havepreviously achieved the desired small wire diameter by drawing processeswhereby the metal or metal alloy is drawn through a hole in a plate or ablock of harder material which is known as a die. This operationconverts the configuration .of thestarting material, for example a rod,to an elongated wire of reduced cross section. The drawing process isrepeated as often as necessary by using dies with successively smallerholes until the desired reduction in cross sectional area is obtained.When working in theultra fine wire area, for example wires having adiameter of one one thousandths of an inch, it has been the commonpractice to employ diamond dies. Such dies are relatively expensive inmanufacture and in use, thus resulting in a greater cost for the ultrafine wire thereby produced. When the desired final wire size is greaterthan four one-thousandths of an inch, it is possible to employ carbidedies and not diamond dies to thereby reduce equipment costs. The carbidedies can be economically and practically used in wire drawing down tofour onethousandths of an inch. With smaller wire diameters, it is theusual practice always to utilize diamond dies.

In the case of drawing ultra fine gold wire, it has been found that thephysical strength of the gold element was such that the wire drawingprocedure could only be utilized to draw gold wire down to twoone-thousandths of an inch by utilizing conventional wire drawingequipment due to the weakness of the material itself. Accordingly, atthe present time, there is no inexpensive method or apparatus capable ofdrawing gold wire as fine as one one-thousandths of an inch.

SUMMARY OF THE INVENTION The present invention relates generally to thefield of forming fine wires, and more particularly, is directed to aprocedure for fabricating ultra-small, pure gold wire of oneone-thousandths of an inch diameter or less in size.

The present invention features a method which starts with a coppersheath of square cross sectional configuration which has a square axialbore provided therein. A square gold or other precious metal bar ofsuitable cross sectional-dimensions to easily slide within the axialbore is formed and placed in position within the axial bore. Thegeometry of the initial components is such that the ratio ofmeasurements of the copper sheath to the gold bar is initially a ratioof at least 5 to l, and preferably is precisely at the ratio of to l.

The assembled copper clad gold bar is entered into suitable squareshaped wire reduction rolls and is reduced sufficiently to mechanicallybond the gold bar to the copper sleeve, thereby creating a compositewire having a ratio of ten to one, copper to gold. Continued reductionof the assembled product isachieved by.employing conventional wirereducing rolls. Steps are taken to change the configuration from squareto round in well known manner.

ple 30 A.W.G., can be reached so that the copper sheath will measure0.010 inches outside diameter. Wires of this diameter can beconveniently drawn by employing carbide dies. The gold core diameterwill remain in the same ratio of 10 to 1, thereby resulting in a goldwire diameter of 0.001 inches. At 31 A.W.G., the sheath diameter will be0.0089 inches and a gold core of 0.00089 inches will result. At 32gauge, the sheath will measure 0.008 inches and a gold core of 0.0008inches will result. At 33 gauge, the sheath diameter will be 0.0071inches and the gold core will be reduced to 0.00071 inches. At 34 gauge,the sheath will measure 0.0063 inches'and a gold core of 0.00063 incheswill result. At 35 gauge, the sheath will measure 0.0056 inches and thegold core of 0.00056 inches will result. At 36 gauge, the sheathdiameter will be 0.005 inches and a gold core of 0.0005 inches willresult.

When the desired gold wire is achieved, the composite material can becut into lengths and the lengths can be placed in a glass container foretching or removing the copper sheath from the finish gold core wire byemploying a suitable acid, for example, nitric or sulphuric acid. Theultra-small pure gold wire thus produced will meet known gold wirestandards, for example ASTM Designation: F72-69 entitled Gold Wire ForSemiconductor Head-Bonding" as published by the American Society ForTesting and Materials.

It is therefore an object of the present invention to provide animproved procedure for fabricating ultrasmall pure gold wire of the typeset forth.

It is another object of the present invention to provide an improvedmethod for fabricating ultra-small pure gold wire by employing a coppersheath and a gold core in an initial ratio of 10 to 1.

It is another object of the present invention to provide a novel methodfor fabricating ultra-small pure gold wire wherein a gold bar is placedwithin a copper sheath having an initial ratio of ten to one, copper togold, and wherein the components are simultaneously reduced by wiredrawing in the same ten to one ratio until the ultra fine wire size isachieved.

It is another object of the present invention to provide a novel methodfor fabricating ultra-small pure gold wire wherein a gold bar isinserted into a copper sheath and the assembly is reduced by drawing tothe ultra fine range, wherein the strength of the copper sheath isemployed to permit gold to be drawn to diameters of 0.001 inches orless.

It is a further object of the present invention to provide a novelmethod of fabricating ultra-small gold wire of 0.001 inches diameter orless wherein the need for diamond dies can be completely eliminated.

It is another object of the present invention to provide a novel methodfor fabricating ultra-small pure gold wire of 0.001 diameter or less insize wherein gold wire is copper clad and the copper cladding has atendency to increase the working characteristics of the compositestructure through increased strength.

As used in this specification, the term ultra-small" may be consideredas those wires having a diameter of 0.001 inches or less.

It is a further object of the present invention to provide a novelmethod for fabricating ultra-small pure gold wire that is simple inprocedure, inexpensive in equipment costs and trouble free in operation.

Other objects and a fuller understanding of the invention will be had byreferring to the following description and claims of a preferredembodiment thereof,

taken in conjunction with the accompanying drawings, wherein likereference characters refer to similar parts throughout the several viewsand in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial, perspective viewof the end of an initial square copper sheath in accordance with thepresent invention.

FIG. 2 is a view similar to FIG. 1 showing a gold bar in the process ofbeing inserted into the central opening of the sheath.

FIG. 3 is a cross sectional view taken along Line 3-3 of FIG. 2, lookingin the direction of the arrows.

FIG. 4 is an enlarged schematic, elevational view showing a reduction inwire gauge size of the composite material.

FIG. 5 is a schematic, elevational view showing one method of removingthe copper sheath from the gold wire.

FIG. 6 is a perspective view'of a spool upon which the ultra-small puregold wire produced in accordance with the present method is being wound.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION Althoughspecific terms are used in the following description for the sake ofclarity, these terms are intended to refer only to the particularstructure of my invention selected for illustration in the drawings andare not intended to define or limit the scope of the invention.

The invention will be described with the sheath to core dimensionalrelationship of 10 to 1. It will be appreciated however, that otherrelationships such as 5 to l or over can be similarly utilized. In orderto practice the present invention, a gold or other precious metal ormetal alloy ingot should be prepared by melting pure gold in aclay-graphite crucible in an oxidizing atmosphere. The melting preciousmetal or alloy is then poured into a graphite split mold at preferablyapproximately 50 F. above the melting point of gold, or approximately ata temperature in the l,950 to 2,000 F range. The mold should preferablybe preheated and an oxidizing atmosphere should be employed during themelting and pouring operations. Slow pouring is advisable to reduce thedangers of cold shuts and surface imperfections. The gold is thenconventionally rolled to reduce the size, but great precautions shouldbe taken to guarantee the cleanliness of the rolls from any metallicobjects. Cleaning must be done every fourth reduction on the wirereducing rolls. At no time should the wire be permitted to rub on themetallic plate, either when entering or exiting the rolls. This cleaningprocess is necessary to remove very small micro particles which may becarried over from the rolling process. In the preferred embodiment, therolling and cleaning processes should be continued until the gold wirebar 14 has been reduced to approximately 0.320 inches square. The goldwire is then cleaned and annealed at 970 F. for 15 minutes.

Separately, a copper sleeve 10 is prepared by either casting ormachining to a square configuration having outside dimensions ofprecisely 3% inches with a longitudinally extending, central, squareopening 12 machined or otherwise provided therein. The square opening 12is formed to a configuration whereby each of the sides measuresprecisely 0.375 inches. The copper sleeve 10. is then annealed in areducing atmosphere such as nitrogen at 1,000 F. for 15 minutes. It isnoteworthy that at no time is the composite goldcopper assembly everannealed together. In this manner, by separately annealing the gold andcopper components, it is possible to avoid any diffusion whatsoever ofgold into copper or copper into gold when the gold bar 14 and coppersheath 10 are brought into contact. Thus, the copper can be readilyremoved by acid treatment as hereinafter more fully set forth when thecomposite article is finished to the desired final size diameter. Theannealed gold bar 14 is then inserted into the square opening 12 of theseparately annealed sheath 10. It will be noted that the side dimensionsof the gold bar 14 are precisely 0.320 inches and the dimensions of theopening 12 are 0.375 inches, thereby permitting an easy, sliding fitwithout the need for employing any tools or other mechanical devices.

The assembled copper clad gold bar is then entered into conventional,square shaped wire reduction rolls (not shown) and is reduced from theoriginal outside measurement of 3.250 inches square to 3.200 inchessquare. In this manner, the dimensions of the opening 12 will be reducedto 0.320 inches to mechanically bond the copper sleeve 10 to the goldbar 14 at a ratio of 10V to 1, copper to gold. The outside dimensions ofthe copper sleeve 10 will then be 3.200 inches on each side and thedimensions of the hole 12 and the gold bar 14 will be precisely 0.320inches on each side, causing a tight mechanical bond.

With the composite material thus bonded, continued reduction on carbidewire reducing rolls 18 can conventionally proceed by standard reductionsin a manner well known to those skilled in the art, until the size of0.325 inches outside measurement is obtained. One end of the assembled,reduced unit can then be forged or otherwise pointed and rounded for alength of approximately 4 inches to a size slightly less than aconventional carbide wire drawing die 18, for example 0.290 inchesdiameter so as to permit the mechanical pull of the elongated wirecombination 16 through the die 18 for its entire length. This operationwill change the shape of the wire 16from square cross-sectionalconfiguration to a partially round cross-sectional configuration 20.

The assembled, partially round unit 20 is then again forged or pointedfor a length of approximately 4 inches to a size slightly less than thenext round shaped carbide wire drawing die, namely a die of 0.257 inchesdiameter. At this stage, the shape of the wire will be changed from itsoriginal square shaped cross-sectional configuration to a perfectlyround shaped copper clad gold wire 22 after having been mechanically,conventionally pulled through the die 18.

The composite round wire 22 is then reduced from the 0.257 inches (No. 2A.W.G.) by A.W.G. reductions on a conventional wire machine (not shown).When 30 A.W.G. is reached by the carbide wire drawing dies (not shown),the copper sheath will measure 0.010 inches outside diameter and a goldcore diameter of 0.001 inches will result. At 31 A.W.G., the outsidediameter of the copper sleeve will measure 0.0089 inches and the goldcore diameter of 0.0089 inches will result. At 32 gage, the outsidediameter will measure 0.008 inches and the gold core will measure 0.0008inches, as shown in the following table:

When the desired final diameter of gold core is reached, the gold wire24 will be finished with the copper sheath 26 still intact. The spooledend is then fed at a rate of approximately feet or more per minute to aconventional, miniature wire straightening machine (not shown) that runsin a rotary motion to straighten the wire. If desired, the compositecopper clad gold wire 22 of reduced diameter can be cut into lengths asrequired and then placed into a glass or other suitable container 28 foretching or otherwise removing the copper sheath 26 from the gold corewire 24 by employing a bath 30 such as nitric acid. The cut lengthsremain in the nitric acid bath 30, a sufficient length of time until allof the copper sheath 26 has been removed. Optionally, the compositecopper clad wire 22 may be continuously fed into the bath 30 byemploying suitable rolls 32, 34, 36 in a manner to automatically andcontinuously remove the copper sheath 26 from the gold wire 24. Ifnecessary, the pure gold, ultra-fine wire 24 can be thoroughly rinsed inconventional manner to remove any etchents and then dried by air priorto use. if desired, the gold wire 24 may be conventionally wound upon afinished wire spool 38 for storage purposes prior to use.

Although I have described the present invention with reference toparticular embodiments therein set forth, it is understood that the.present disclosure has been made only by way of example and thatnumerous changes in the details of construction may be resorted towithout departing from the spirit and scope of the invention. Thus, thescope of the invention should not be limited by the foregoingspecification, but rather by the scope of the claims appended hereto.

1 claim:

1. The method of fabricating ultra-small precious metal or metal alloywire comprising the steps of A. forming a copper sleeve having a firstcrosssectional size and annealing the sleeve,

1. said copper sleeve being formed with an axially aligned openinghaving a second cross-sectional size;

B. forming a core of precious metal or metal alloy having a third crosssectional size and annealing the core, said annealing being carried outseparately from annealing the sleeve,

1. the ratio of the first cross-sectional size to the thirdcross-sectional size being at least five to one,

2. the second cross sectional size being formed slightly larger than thethird cross-sectional size;

C. inserting the previously annealed core into the opening and thenreducing the second crosssectional size to equal the thirdcross-sectional size to mechanically bond the core to the sleeve;

D. reducing the cross-sectional size of the sleeve and the crosssectional size of the core in the same ratio as the initial sizes bysuccessive size reductions until the core is reduced to the ultra-smallwire size range, and

E. removing the sleeve chemically from the core to produce anultra-small precious metal wire.

2. The method of claim 1 wherein the ratio of sleeve to core is ten toone.

3. The method of claim 1 wherein the copper sleeve, the opening and thecore are all initially formed to square cross-sectional configurations.

4. The method of claim 3 wherein the sleeve and core combination isintroduced to successively smaller sized carbide wire drawing dies toachieve smaller wire sizes.

provide overall bonding.

1. The method of fabricating ultra-small precious metal or metal alloywire comprising the steps of A. forming a copper sleeve having a firstcross-sectional size and annealing the sleeve,
 1. said copper sleevebeing formed with an axially aligned opening having a secondcross-sectional size; B. forming a core of precious metal or metal alloyhaving a third cross sectional size and annealing the core, saidannealing being carried out separately from annealing the sleeve,
 1. theratio of the first cross-sectional size to the third cross-sectionalsize being at least five to one,
 2. the second cross sectional sizebeing formed slightly larger than the third cross-sectional size; C.inserting the previously annealed core into the opening and thenreducing the second cross-sectional size to equal the thirdcross-sectional size to mechanically bond the core to the sleeve; D.reducing the cross-sectional size of the sleeve and the cross sectionalsize of the core in the same ratio as the initial sizes by successivesize reductions until the core is reduced to the ultra-small wire sizerange, and E. removing the sleeve chemically from the core to produce anultra-small precious metal wire.
 2. The method of claim 1 wherein theratio of sleeve to core is ten to one.
 2. the second cross sectionalsize being formed slightly larger than the third cross-sectional size;C. inserting the previously annealed core into the opening and thenreducing the second cross-sectional size to equal the thirdcross-sectional size to mechanically bond the core to the sleeve; D.reducing the cross-sectional size of the sleeve and the cross sectionalsize of the core in the same ratio as the initial sizes by successivesize reductions until the core is reduced to the ultra-small wire sizerange, and E. removing the sleeve chemically from the core to produce anultra-small precious metal wire.
 3. The method of claim 1 wherein thecopper sleeve, the opening and the core are all initially formed tosquare cross-sectional configurations.
 4. The method of claim 3 whereinthe sleeve and core combination is introduced to successively smallersized carbide wire drawing dies to achieve smaller wire sizes.
 5. Themethod of claim 4 wherein the sleeve and core combination is drawn to 36A.W.G. without employing diamond wire drawing dies.
 6. The method ofclaim 5 and the additional step of cleaning the sleeve and corecombination at least as often as every fourth reduction on the wiredrawing dies.
 7. The method of claim 1 wherein the reduction of thesecond cross sectional size is carried out simultaneously throughout thelength of the copper sleeve to provide overall bonding.